NK cells cultured with pDCs, in the presence of CpG-A, kill iMDDCs but not pDCs. Freshly isolated NK cells were cocultured with autologous pDCs and CpG-A in the presence or in the absence of a mixture of neutralizing antibodies specific for IFN-α and for its receptor (indicated as aIFN). After 24 hours of coculture NK cells were assessed for their cytotoxic activity against allogeneic, freshly blood-derived pDCs (A) or against allogeneic iMDDCs (B) in a 4-hour ⁵¹Cr-release assay. As a control, the same NK cells, activated or not with rhIL-2 for 24 hours, were tested for cytotoxicity against either pDCs or iMDDCs. The effector-to-target (E/T) ratio was 20:1. Each value represents the mean of triplicate experiments. The SD did not exceed 5%. Data are representative of at least 6 different experiments.